A typical multi-speed bicycle has a chain drive, which connects a pedal-driven crank to a driven wheel. The chain drive may have several front sprockets (chain rings) of different pitch diameters and several rear sprockets of different pitch diameters. The front sprockets are connected to the crank and rotate with the pedals. The rear sprockets are coupled to the driven wheel of the bicycle. A chain couples one of the front sprockets to one of the rear sprockets. Different gear ratios can be selected by moving the chain so that it couples a selected front sprocket to a selected rear sprocket.
Such bicycles typically have cable-actuated front and rear derailleurs. A cyclist can operate the front derailleur to move the chain to a selected one of the front sprockets. The cyclist can operate the rear derailleur to move the chain to a selected one of the rear sprockets.
There are various handlebar mounted mechanisms, which a cyclist can use to operate the front and rear derailleurs to achieve a desired gear ratio. For example, some bicycles have a pivotable lever mounted on each side of the handle bar. One lever is connected to a cable that operates the front derailleur and the other is connected to a cable that operates the rear derailleur. A cyclist can select a desired gear ratio by pivoting the levers.
The GRIP SHIFT™ shifting mechanism provides a pair of handle-bar mounted collars. One collar is mounted to a bicycle's right handlebar and the other to the bicycle's left handlebar. One of the collars is connected to a cable that operates the front derailleur. The other collar is connected to a cable that operates the rear derailleur. A cyclist can rotate the collars relative to the bicycle handlebar to select a desired gear ratio.
Cirami, U.S. Pat. No. 4,201,095, describes a bicycle gear-shifter having a single lever that operates both front and rear derailleurs to yield a progressive and programmed series of gear ratios. The Cirami mechanism has two flat plane cams. Intermediate drive ratios are obtained in consecutive increments ordered from the lowest to the highest drive ratio positions of the lever. Cirami proposes a shift pattern that avoids gear ratios that result in cross chaining.
Ross, U.S. Pat. No. 4,279,174, discloses another bicycle gear shifter which permits a cyclist to operate front and rear derailleurs by manipulating a single control. The Ross shifter requires two types of derailleurs: a spring-biased front derailleur and a “push-pull” rear derailleur. The Ross shifter is constructed to provide a progressive shift pattern. Ross describes a shift pattern in which four changes involve shifting or changing the position of both derailleurs simultaneously to provide a progressive series of gear ratios.
Watarai, U.S. Pat. No. 5,577,969, discloses an electronic apparatus for controlling both the front and rear derailleurs of a bicycle. A cyclist can cause the apparatus to shift between gears by operating a lever.
Brix, U.S. Pat. No. 1,114,400, describes a mechanism for adjusting the positions of rods, which control the spark control, throttle, muffler control and engine clutch of a motorcycle. Each control rod is independently adjusted. The Brix mechanism employs two cylindrical sleeves, which are coupled to, and located within, the motorcycle handgrip. Each sleeve is associated with one of the control rods and features a helical groove in its cylindrical surface. When the rider rotates the handgrip, one sleeve is rotated, while the other is prevented from rotating. A cam follower travels in the helical groove of the rotating sleeve, causing longitudinal movement of the associated control rod.
Savard, U.S. Pat. No. 5, 970,816, describes a bicycle gear shifter, which provides a mechanism for controlling both front and rear derailleurs. The mechanism is operated by rotating one handgrip. A cylindrical barrel is attached to the inner end of the handgrip. The barrel has a track on each of its inner and outer faces. Cables from the front and rear derailleurs are each connected to a corresponding one of a pair of cam followers. The cam followers each slide in one of the tracks. When the barrel is rotated, the members move the derailleur cables to select different gear ratios. The cam followers and follower guides are located close to each other on the outside of the handlebar. This results in a large bulbous assembly on the inboard side of the separate rotatable handgrip. A separate detent mechanism holds the collar in a position corresponding to the selected gear ratio. Like Cirami, Ross, and others, the Savard mechanism may be constructed to provide an optimal shift pattern in which undesirable or redundant gear combinations are avoided. A mechanism like the Savard mechanism is marketed by EGS of France under the trademark SYNCHRO SHIFT™. The SYNCHRO SHIFT™ mechanism is undesirably bulky. Its size makes it incompatible with standard bicycle brake levers.
Socard, U.S. Pat. No. 5,447,475 discloses two separate and quite different bicycle gear shifting mechanisms. The mechanisms provide an optimal shift pattern that avoids cross chaining. The mechanisms are actuated via a cable that links to a handle bar mounted shift mechanism which provides two levers; one for shifting up and the other for shifting down. The mechanisms include a cam which rotates 90 degrees for each shift.
Wechsler, U.S. Pat. No. 4,530,678, discloses a bicycle gear shifting mechanism that uses a cylindrical cam with a cam follower to control a rear derailleur. The cam is integrated into the rear derailleur mechanism and has cam grooves cut into its exterior surface. A second rotary cam is used to control a front derailleur. The second cam is integrated into the front derailleur. There is a cable that mechanically connects the front and rear derailleurs so that as one moves, the other also moves. Wechsler's front derailleur cam is shaped to cause the front derailleur to alternate between a large and small chain ring with each consecutive shift.
Patterson, U.S. Pat. No. 4,900,291 discloses a bicycle gear shifting mechanism which has a rotatable handgrip actuator cam that is coupled via a cable to a derailleur mechanism. Separate independent cams are provided for controlling front and rear derailleurs. A cam surface on an edge of each cam abuts against a fixed post. The cam surface has peaks and valleys and uses cable tension to index the shifter. As a cam is rotated the cam slides longitudinally. An end of the cable is attached to the cam.
Ethington, U.S. Pat. No. 5,681,234, discloses an “Automatic Transmission Shifter For Velocipedes” that employs speed and force sensors as well as a programmable logic controller and two servo motors to automatically shift a bicycle transmission according to operating conditions. Ethington discloses a shift pattern that uses all gears in an ascending sequence. Many of the speed changes involve shifting both front and rear derailleurs simultaneously.
Nier, U.S. Pat. No. 5,803,848, discloses a shifter system that employs a shift pattern that is identical to the one used by Socard and others. This system uses flat radial cams that are linked and rotatably mounted on a handle bar. Nier's system combines a cam which operates the front derailleur by way of a mechanical linkage and two other cams with nodes that actuate electric motors to either pull or release the rear derailleur by predetermined amounts. The use of these three cams in combination results in an optimal shift pattern.
Lahat, U.S. Pat. No. 5,865,062, discloses several mechanisms that control both front and rear derailleurs to achieve an optimal shift pattern. These mechanisms show both single cylinders with two cam surfaces and several arrangements of dual cylinders with single cam surfaces. In all cases the cams and followers are located on the exterior of the handlebar. In some cases, the cam and follower assembly are mounted in a separate casing and are not rotatably mounted on the handlebar. In all cases, the mechanisms are “aimed at synchronously controlling both front and rear derailleurs to achieve a predetermined sequential combinations of front and rear gears.
Despite the long history of bicycle development and the large variety of shifting mechanisms that have been proposed for bicycles, there remains a need for practical gear shifting mechanisms suitable for use in bicycles and other pedal-powered vehicles. There is a particular need for such mechanisms, which permit a user to select a desired gear ratio without needing to separately control two shifting mechanisms.